mailmap: add entry for email addresses

Redirect email addresses from git log to the mainly used ones
for Alexei and myself such that it is consistent with the ones
in MAINTAINERS file. Useful in particular when git mailmap is
enabled on broader scope, for example:

  $ git config --global log.mailmap true

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>